The present disclosure relates to a vapor deposition mask substrate, a method for manufacturing a vapor deposition mask substrate, a method for manufacturing a vapor deposition mask, and a method for manufacturing a display device.
A vapor deposition mask includes a first surface, a second surface, and holes extending through the first and second surfaces. The first surface faces a target such as a substrate, and the second surface is opposite to the first surface. The holes each include a first opening, which is located in the first surface, and a second opening, which is located in the second surface. The vapor deposition material entering the holes through the second openings forms on the target a pattern corresponding to the position and shape of the first openings (see Japanese Laid-Open Patent Publication No. 2015-055007, for example).
Each hole of the vapor deposition mask has a cross-sectional area that increases from the first opening toward the second opening. This increases the amount of vapor deposition material entering the hole through the second opening so that an adequate amount of vapor deposition material reaches the first opening. However, at least some of the vapor deposition material entering the hole through the second opening adheres to the wall surface defining the hole, failing to reach the first opening. The vapor deposition material adhering to the wall surface may prevent other vapor deposition material from passing through the hole, lowering the dimensional accuracy of the pattern.
To reduce the volume of vapor deposition material adhering to the wall surfaces, a structure has been contemplated in which the thickness of the vapor deposition mask is reduced to reduce the areas of the wall surfaces. In order to reduce the thickness of the vapor deposition mask, a technique has been contemplated that reduces the thickness of the metal sheet used as the substrate for manufacturing the vapor deposition mask.
However, in the process of etching the metal sheet to form holes, a smaller thickness of the metal sheet results in a smaller volume of metal to be removed. This narrows the permissible ranges in the processing conditions, such as the duration for which etchant is supplied to the metal sheet and the temperature of the supplied etchant. This increases the difficulty in achieving the required dimensional accuracy of the first and second openings. In particular, the manufacturing of metal sheet involves a rolling step, in which the base material is drawn with rolls, or an electrolysis step, in which the metal sheet deposited on an electrode is peeled off from the electrode. Accordingly, the metal sheet has an undulated shape. In the metal sheet having such a shape, the duration for which the ridges in the undulated shape are in contact with the etchant differs greatly from that of the valleys in the undulated shape. This aggravates the reduced accuracy resulting from the narrowed permissible ranges described above. As such, although a thinner vapor deposition mask reduces the amount of vapor deposition material adhering to the wall surfaces and thereby increases the dimensional accuracy of the patterns in repeated vapor deposition, such a vapor deposition mask involves another problem that the required dimensional accuracy of the pattern in each vapor deposition is difficult to achieve.